This invention relates generally to the cold-rolling of metals and is concerned with the production of superior quality strip in high yields while reducing the lubrication costs of the rolling operation. More specifically, the invention relates primarily to the operation of steel rolling mills employing oil-in-water emulsions as lubricants and defines a unique method for reducing the consumption of oil in any such system by controlling the stability of the emulsion within preselected limits.
The use of oil-in-water emulsions as lubricants in present-day rolling mills has become quite conventional. The typical emulsion utilized in such an operation comprises an aqueous dispersion of a blend of oils, usually mineral oil and natural oils such as tallow (which are essentially esters of glycerol and long chain fatty acids) along with nonionic and/or anionic emulsifying agents. The nature and concentration of oils in any such emulsion will be determined by the frictional and/or lubricity requirements of the process as required by the specifications of the steel involved, the operating conditions, the desired reduction and the final gage. However, in the past the methods for determining optimum oil concentrations have been rather imprecise, in many cases resulting in an unnecessary and expensive consumption of oil in the operation. It is an object of this invention to diminish such oil loss.
Also in the cold rolling of steel strip, particularly in the production of what is commonly known as double reduced or thin tinplate, it is common to develop numerous problems which can be attributed to a breakdown of the emulsion after an initial period of use. Such problems include the necessity of exceptionally high loads, i.e., pressure, on the rolls, as well as irregular "wetting" of the steel strip and the resulting formation of localized pockets of lubricant which under the hydraulic pressure of the rolls causes surface irregularities and mottling. It is a further object of this invention to substantially overcome these difficulties.
The above objects and others which will become apparent in the ensuing discussion are achieved in the present discovery of a relationship between emulsion stability, oil concentration and plate-out rate of the lubricant.